session2: include desktop and desktop-local streams in docstring

darcs-hash:20090430114126-b2873-259466dd3472a3250319a97df649609f9237758c
sip_session2: use the same titles for desktop streams in incoming case as in outgoing

darcs-hash:20090430114152-b2873-00372e328d555f9bb74351211dc8ef5c42bb3f0f